1. Field of the Invention
The present invention relates to a coordinates detecting apparatus and, more specifically, to a coordinates detecting apparatus for detecting 2-or 3-dimensional coordinates.
2. Description of the Background Art
A 2-dimensional digitizer for detecting coordinates of a position designated by a pen, a finger or the like has been proposed as a typical coordinates detecting apparatus. In the 2-dimensional digitizer, an X data signal for specifying the X coordinate and a Y data signal for specifying the Y coordinate are generated, the generated data signals are corrected, and the coordinates of the designated position are detected. Here, various methods including resistive film sensing method, electromagnetic induction method, electrostatic coupling method, ultrasonic method, oscillator method and so on may be utilized for the coordinates input sensor. The X and Y data signals may be subjected to correction through hardware or software processing or noise reduction.
Japanese Patent Laying-Open No. 9-62450 or 9-101853 discloses a method of determining irregularity in difference of distance between samples in a tablet as the 2-dimensional digitizer utilizing the resistive film pressure sensing method. According to this method, noises involved in the X and Y data signals can be removed to some extent. The noise, however, cannot be removed completely and always remains either in the X or Y data signal. If the level of noise removal is set higher to completely remove noise, accurate data signal could not be obtained
The inventors have found through various experiments that the mechanism of noise generation differs between X and Y directions. The above described prior art technique proposes correction or filtering not considering such difference, which is the reason why there is always noise remaining either in the X or Y data signal. The inventors clarified the mechanism of noise generation, and developed a coordinates detecting apparatus capable of almost fully removing noises both in the X and Y directions and capable of detecting accurate coordinates.
Possible causes of difference in noise in the X and Y directions include difference in radiation noise reaching from the liquid crystal display (LCD) below the tablet to the transparent conductive films for specifying X and Y coordinates, difference in length and width of the tablet, difference in sheet resistance of the transparent conductive films for specifying X and Y coordinates, and difference in structure of the transparent conductive films for specifying X and Y coordinates.
An object of the present invention is to provide a coordinate detecting apparatus capable of detecting accurate coordinates almost free of any noise in any of X, Y and Z directions.
According to the present invention, the apparatus for detecting a first coordinate and a second coordinate independent from the first coordinate includes a sensor unit and a correcting unit. The sensor unit is disposed to generate a first data signal for specifying the first coordinate, and a second data signal for specifying the second coordinate. The correcting unit is coupled to receive the first and second data signals and disposed to correct the first data signal using an adjustable first parameter, and to correct the second data signal using a second parameter adjustable independent from the first parameter.
Preferably, the correcting unit includes first and second correcting circuits. The first correcting circuit is coupled to receive the first data signal and disposed to correct the first data signal using the first parameter. The second correcting circuit is coupled to receive the second data signal and disposed to correct the second data signal using the second parameter.
More preferably, the first correcting circuit includes a first filter circuit disposed to remove noise of the first data signal. The second correcting circuit includes a second filter circuit disposed to remove the noise of the second data signal.
Preferably, the correcting unit includes means for setting first and second parameters independently, and means for calculating the first coordinate based on the first data signal using the first parameter, and the second coordinate based on the second data signal using the second parameter.
In the coordinates detecting apparatus structured as described above, the first data signal is corrected by the first parameter, and the second data signal is corrected by the second parameter independently. As the first and second parameters can be adjusted independent from each other, it is possible to optimally correct the first data signal and optimally correct the second data signal. As a result, both the first and second coordinates can be detected at high accuracy.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.